Full coverage of a second generation (2G) or third generation (3G) network, such as Global System for Mobile Communications (GSM) or Wideband Code Division Multiple Access (WCDMA) has been basically implemented.
With development of Long Term Evolution (LTE) network technologies, LTE networks have covered some urban areas and traffic hot spot areas. In this way, on current communications networks, the LTE networks coexist with the 2G or 3G network.
During a call, user equipment (UE) may enter a 2G or 3G network from an LTE network, and handover from a packet switched (PS) domain to a circuit switched (CS) domain is required due to different bearer mechanisms of the LTE network and the 2G or 3G network, where interruption of a voice call may occur, and consequently, continuity of a voice call of a user is affected.
Circuit switched fallback (CSFB) is that when UE covered by LTE network processes a voice service, the UE first falls back to a network that has a CS domain, and processes the voice service on the network that has the CS domain, thereby fulfilling an objective of reusing an existing CS domain device to provide a traditional voice service for a user on the LTE network. In the prior art, the UE needs to be handed over from the LTE network to a PS domain of the 2G or 3G network, or to be redirected from the LTE network to the 2G or 3G network, and then initiates, on the 2G or 3G network, a connection to the CS domain. In the prior art, even though the UE and the network can support handover from the LTE network to the CS domain of the 2G or 3G network, the UE needs to be moved to the PS domain of the 2G or 3G network so as to initiate a voice call, which causes relatively long duration of an entire voice call and poor user experience.